1. Field of the Invention
The present invention relates to a steering system for a boat. More particularly, the invention relates to a boat steering system with an electric actuator.
2. Description of the Related Art
In a boat having an outboard motor mounted on a stern of a boat hull, it is known to have a steering system in which an electric actuator such as an electric motor applies a steering force to the outboard motor in response to an electric signal generated by operation of a steering wheel, as described in Japanese Patent Document No. JP-B-2959044. The load applied to the electric actuator for steering the outboard motor is referred to as “steering load”. If an excessive drive current is provided to the electric motor when the steering load is small, a control amount may overshoot a target value and steering characteristics deteriorate as shown in FIG. 9(a).
In Patent Document JP-A-2006-69408, a steering system is disclosed in which the drive current provided to an electric motor is decreased when the boat cruises at a low speed. Here, the steering load is greater when the boat cruises at a high speed than when the boat cruises at a low speed. Therefore, the torque output by the electric motor in steering increases at high speed compared to low speed cruising.
However, the art does not teach a construction for increasing steering torque when needed during cruising, and torque requirements change during boat cruising. As such, a significant time lag exists between steering inputs from the steering wheel and actual steering of the outboard motor.